A new, tentative congressional compromise will impose strict conditions on President Reagan's controversial drug-testing program, almost certainly delaying its implementation and holding down the number of federal employes to be tested.

Meanwhile, the administration was pressing hard yesterday for modifications in the compromise that would allow the Transportation Department to begin testing air traffic controllers before the peak summer travel season, according to the Office of Personnel Management.

Supporters of drug testing hailed the compromise, saying it would allow testing to move forward, albeit glacially, while protecting employes' rights. Opponents said drug testing had been "killed . . . with kindness," going so far to protect privacy and accuracy -- and thus elevating the costs -- that many agencies will back away from the program.

The compromise requires that:

Urine testing procedures be "equivalent to the standards governing evidence in criminal proceedings," a demanding and expensive proposition.

"Guidelines" for conducting tests be issued as "regulations," which carry notification and comment period requirements and can be subject to court suits.

Efforts be made to rehabilitate an employe found to be using drugs before the employe can be fired.

An agency's detailed analysis of the positions designated for testing -- and the reasons for their designation -- be submitted to Congress before testing can begin.

The compromise, worked out by aides to Rep. Steny H. Hoyer (D-Md.) and Sens. Dennis DeConcini (D-Ariz.), Pete V. Dominici (R-N.M.) and Barbara A. Mikulski (D-Md.), was attached to a routine House appropriations bill late Wednesday and quickly became the subject of administration damage-control efforts.

The administration objects to a provision that appears to require that an elaborate drug-testing plan covering all agencies be in place before any testing can begin. This provision, opponents say, would allow a Cabinet secretary who opposes testing to withhold approval of the plan and wield veto power over the entire program.

In April, the House approved a ban on funding for drug testing when it passed its version of the supplemental appropriations bill for programs that will run out of money before the fiscal year ends.

The Senate voted Friday to allow testing only after the administration certifies that specified safety, quality-control and employe-rights standards had been met. A House-Senate conference on the bill is scheduled for Tuesday.

Reagan is thought unlikely to veto the $10 billion bill because of the drug-testing issue, since the bill includes $6.7 billion to continue crop subsidies and funds for military health benefits, a federal pay raise and retirement costs.

The critical issue in the bill for the administration is said to be an arms control provision in the House version that orders resumed compliance with SALT II as long as the Soviets comply and limits nuclear weapons testing.

The administration reportedly has signaled that if the arms control provisions are removed, it will sign the bill, regardless of the drug-testing language.

The president ordered federal drug testing last September and asked OPM and the Department of Health and Human Services to develop testing guidelines. OPM issued rules last year allowing agencies wide latitude in determining whom to test and for what drugs.

HHS followed up in February with guidelines requiring rigid monitoring of employes, the testing of temperatures of urine samples and the placement of blue dye in designated federal toilets to prevent workers from cheating by diluting their samples with water from the bowl.

Under the congressional compromise, the guidelines will have to become regulations, roughly as different from guidelines as an order is from a suggestion.

The National Treasury Employes Union has asked the Supreme Court to block drug testing of U.S. Customs Service workers, but the union's request for a temporary stay of a lower court order was turned down Monday.